Nowadays, head-mounted display apparatuses (or head-mounted devices) are increasingly being used for a number of purposes such as gaming, education, military training, medicine, and so forth. In such an instance, a simulated environment is presented to a user when he/she wears such a head-mounted display apparatus. The head-mounted display apparatus employs contemporary techniques such as stereoscopy to provide the user with a feeling of complete involvement (namely, immersion) within the simulated environment. Therefore, the simulated environment provides the user with an enhanced perception of reality around him/her. Furthermore, the simulated environment could be a fully virtual environment (namely, virtual reality) as well as a real world environment including virtual objects overlaid thereon (namely, augmented reality).
Lately, gaze-tracking (namely, eye tracking) techniques are being employed to determine a direction of gaze of the user, whilst the user uses the head-mounted display apparatus. Generally, in such gaze-tracking techniques, an illumination source is employed for emitting light towards the user's eyes, and an imaging device (for example, such as a camera) is employed for capturing an image depicting pupils of the user's eyes and reflection(s) of the emitted light from the user's eyes. Consequently, the captured image is employed to determine the gaze direction of the user.
However, there exist limitations associated with implementation of such gaze-tracking techniques. In other words, there exist several optical design constraints associated with equipment for implementing such gaze-tracking techniques. Firstly, the imaging device is required to be arranged outside, or at a peripheral region of the head-mounted display apparatus's field of view. However, for proper imaging, the imaging device needs to be arranged close to the user's eyes, for example, such as a few centimetres away from the user's eyes. In such an instance, the imaging device is required to be arranged within the head-mounted display apparatus, or in frame(s) of the head-mounted display apparatus. Secondly, a position of the head-mounted display apparatus with respect to the user's eyes is not constant, since the head-mounted display apparatus may move (or get displaced) during use. Therefore, both the equipment for implementing the gaze-tracking techniques, and equipment (for example, such as displays, projectors, and so forth) for rendering images of the simulated environment require precise calibration. Thirdly, if the user wears spectacles whilst using the head-mounted display apparatus, the reflection(s) of the emitted light from the user's eyes gets reflected from lenses of the spectacles. Such reflections need to be recognized and filtered out for determining the gaze direction of the user.
Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks associated with conventional equipment and techniques for gaze-tracking.